1. Field of the Invention
The present invention relates to an orthogonal frequency division multiplex (OFDM) signal demodulator circuit and an OFDM demodulating method, which demodulate an OFDM signal received by a tuner.
2. Description of the Related Art
The orthogonal frequency division multiplexing (OFDM) system, by which a plurality of carriers (carrier waves) can be multiplexed to be transmitted and received, is used as a modulation system in the terrestrial digital television broadcasting.
Because the broadcast radio waves of the OFDM system are feeble, it is necessary to amplify the signals by an automatic gain control (AGC) amplifying circuit or the like in a tuner unit.
However, an amplification of a signal in the tuner unit is accompanied by generation of nonlinear distortion owing to transient phenomena or the like of various analog devices constituting the tuner unit. Then, the generated nonlinear distortion is superimposed on the signal, and the C/N value of an output signal of the tuner unit is deteriorated.
Moreover, because the signal having a deteriorated C/N value is inputted into a demodulating unit, a rate of the signals which are not demodulated in the demodulating unit to be regarded as errors increases, and consequently the receiving performance of the tuner unit has been influenced by the increased rate.
Moreover, when an amplification degree by the AGC (variable gain amplifier) becomes larger, the degree of nonlinear distortion generated in the tuner becomes larger, and a phase changes from that of an input signal. Then, the changed phase is generated as phase distortion. Consequently, the C/N value of the output signal of the tuner unit is further deteriorated, and the receiving performance is further influenced by the deterioration of the C/N value.